Die extrem große Bandbreite, die UWB-Systeme zur Übertragung von Daten nutzen können, ermöglicht theoretisch eine sehr hohe Datenrate. Eine mögliche Umsetzung der UWB-Technologie ist die sogenannte Multiband-Impuls-Radio-Architektur (MIRA). Dieses UWB-System basiert auf der Übertragung von Daten mittels kurzer Impulse parallel in mehreren Frequenzbändern. Als Empfänger kommen einfache Energiedetektoren zum Einsatz. Diese Komponenten haben entscheidenden Einfluss auf die Leistungsfähigkeit des gesamten Systems. Deshalb liegt der Schwerpunkt dieser Arbeit auf der Untersuchung der Leistungsfähigkeit und im speziellen der Herleitung der Bitfehlerwahrscheinlichkeiten für Energiedetektoren in unterschiedlichen UWB-Kanälen. Aufgrund des sehr einfachen Aufbaus eines Energiedetektors wird dieser auch in vielen anderen Bereichen eingesetzt. So werden Energiedetektoren zur Detektion von freien Bereichen im Übertragungsspektrum bei Cognitive Radio und für weitere unterschiedliche Übertragungssysteme wie z.B. Sensorsysteme mit geringer Datenrate und Übertragungssysteme die zusätzlich Ortung ermöglichen, genutzt.

In this thesis, symbol timing recovery based on matched filtering in Gaussian Minimum Shift Keying (GMSK) with bandwidth-bit period product (BT) of 0.3 is investigated. GMSK is the standard modulation type for GSM. Although GMSK modulation is non-linear, it is approximated to Offset Quadrature Amplitude Modulation (OQAM), which is a linear modulation, so that Maximum Likelihood Sequence Estimation (MLSE) method is possible in the receiver part. In this study Typical Urban (TU) channel model developed in COST 207 is used. Two methods are developed on the construction of the matched filter. In order to obtain timing recovery for GMSK signals, these methods are investigated. The fractional time delays are acquired by using interpolation and an iterative maximum search process. The performance of the proposed symbol timing recovery (STR) scheme is assessed by using computer simulations. It is observed that the STR tracks the variations of the frequency selective multipath fading channels almost the same as the Mazo criterion.

Multiple-input multiple-output (MIMO) systems have received much attention due to their multiplexing and diversity capabilities. It is possible to obtain remarkable improvement in spectral efficiency for wireless systems by using MIMO based schemes. However, sophisticated equalization and decoding structures are required for reliable communication at high rates. In this thesis, capacity achieving practical transceiver structures are proposed for MIMO wireless channels depending on the availability of channel state information at the transmitter (CSIT). First, an adaptive MIMO scheme based on the use of quantized CSIT and reduced precoding idea is proposed. With the help of a very tight analytical upper bound obtained for limited rate feedback (LRF) MIMO capacity, it is possible to construct an adaptive scheme varying the number of beamformers used according to the average SNR value. It is shown that this strategy always results in a significantly higher achievable rate than that of the schemes which does not use CSIT, if the number of transmit antennas is greater than that of receive antennas. Secondly, it is known that the use of CSIT does not bring significant improvement over capacity, when similar number of transmit and receive antennas are used / on the other hand, it reduces the complexity of demodulation at the receiver by converting the channel into noninterfering subchannels. However, it is shown in this thesis that it is still possible to achieve a performance very close to the outage probability and exploit the space-frequency diversity benefits of the wireless fading channel without compromising the receiver complexity, even if the CSIT is not used. The proposed receiver structure is based on iterative forward and backward filtering to suppress the interference both in time and space followed by a spacetime decoder. The rotation of multidimensional constellations for block fading channels and the single-carrier frequency domain equalization (SC-FDE) technique for wideband MIMO channels are studied as example applications.

This thesis paper proposes a Medium Access Control (MAC) protocol for wireless networks, termed as CD-MMAC that utilizes multiple channels and incorporates opportunistic cooperative diversity dynamically to improve its performance. The IEEE 802.11b standard protocol allows the use of multiple channels available at the physical layer but its MAC protocol is designed only for a single channel. The proposed protocol utilizes multiple channels by using single interface and incorporates opportunistic cooperative diversity by using cross-layer MAC. The new protocol leverages the multi-rate capability of IEEE 802.11b and allows wireless nodes far away from destination node to transmit at a higher rate by using intermediate nodes as a relays. The protocol improves network throughput and packet delivery ratio significantly and reduces packet delay. The performance improvement is further evaluated by simulation and analysis. / sabbir@linuxmail.org

This diploma thesis deals with the analysis of the IEEE 802.11ah wireless communication system. For such a purpose, an appropriate simulation model in program environment MATLAB is created. The first part of thesis focuses on the IEEE 802.11 standard. Basic blocks of the transmitter and receiver are described. Attention is also devoted on the brief description of considered transmission channels. The second part contains the description of the proposed and realized simulation model in MATLAB. Individual blocks of the simulation model are described in details. Finally, the obtained simulation results are evaluated and discussed.

MIMO systems are mainly used in application for wireless communication. Their principle is to use a large number of antennas for transmition and the reception of a signal. The core of these systems is to use space-time coding and either block or trellis space-time code. In the future, it is assumed enormous enlargement MIMO systems in many applications

No description available.

While the capacity of multiple-input multiple-output (MIMO) systems has been explored in considerable detail, virtually all literature on this topic ignores electromagnetic considerations. This dissertation explores electromagnetic effects on the capacity performance of these multi-antenna architectures. Specifically, it examines the impact of superdirectivity for compact antenna arrays, the effect of antenna mutual coupling, and MIMO performance of multi-mode optical fiber with non-linear detection. Superdirectivity can lead to abnormally large capacity bounds in a MIMO communication system, especially when the antennas are placed close together. Because superdirective behavior is difficult to achieve in practice, this work formulates an approach for limiting the impact of superdirectivity by introducing finite ohmic loss into the capacity expressions. Results show that even a small amount of ohmic loss significantly affects the achievable system capacity and suppresses superdirective solutions. This formulation allows a more detailed examination of the capacity of MIMO systems for compact arrays. For channels which do not vary in time, placing antennas closer together generally reduces the system capacity. However, recent work has demonstrated that for a MIMO system operating in a fast fading environment where the transmitter and receiver know the channel covariance information, the capacity increases as antennas are placed near each other due to an increase in spatial correlation. Analysis of this behavior illustrates that when these capacity gains (due to closely spaced antennas) are observed the radiated power is also increased. Constraining the radiated power leads to superdirective solutions in which the ohmic loss constraint developed must be used to properly determine the capacity behavior of this system. Application of this constraint then leads to an optimum antenna spacing in contrast to the findings of previous research which indicate that antennas should be as close together as possible. Additionally, this section provides an analysis regarding the number of spatial modes that can be used for various system configurations. Recent research has shown that it is possible for MIMO communication techniques to be used with multimode optical fibers to increase the available distance-bandwidth. However, implementation of traditional MIMO schemes requires the use of coherent optical detection which can lead to high system complexity and cost. This dissertation proposes a multimode fiber MIMO system architecture which allows simultaneous transmission of unique streams to different users on the same fiber while using incoherent detection with amplitude and phase modulation at the transmitter. The resulting capacity scales nearly linearly with the number of transmitters and receivers. Because the architecture requires channel state information at the transmitter, a training scheme appropriate for use with optical intensity detection is also discussed.

Power allocation algorithms that determine how much power should be allocated to pilot and data symbols play an important role in addressing the trade-off between accurate channel estimation and high high spectral efficiency for data symbols in the presence of time-varying fading channels. Dealing with this trade-off is highly non-trivial when the channel changes or ages rapidly in time. Specifically, channel aging renders the often used assumption that the channel parameters can be regarded constant between channel estimation instances invalid. Previous works have addressed the problem of the pilot spacing problem for Rayleigh fading channels. In this work, a power control algorithm is developed for both Rayleigh fading and Rician fading channels to deal with the above trade-off. Specifically, in this report, the uplink channel of a multi-user multiple input multiple output system is investigated. The fading channel is estimated by a suitable auto-regressive model using the associated auto-correlation function. Then the signal-to-interference-plus-noise ratio and spectral efficiency are calculated as a function of the power allocation ratio and other parameters of the communication network. The proposed power control algorithm is designed to find the upper bound of the spectral efficiency. As application examples, two uncrewed aerial vehicle networks are also modeled, in which the performance of the proposed power control algorithm is simulated to find how the parameters of the network will influence the algorithm results. Our investigation shows that the proposed power control algorithm performs well in the presence of fading communication channels and outperforms the benchmark case of equal power allocation between pilot and data symbols. / Effektallokeringsalgoritmen som bestämmer hur mycket effekt som ska allokeras till pilotsymboler och datasymboler är mycket viktig för att fånga avvägningen mellan korrekt kanaluppskattning och ett högt signal till störnings plus brusförhållande för en tidsvarierande fädning kanal. Tidigare arbete har löst problemet med pilotavstånds-problemet för Rayleigh fädning kanaler. I detta arbete genereras effektstyrnings-algoritmen för både Rayleigh fading och Rician fädning kanaler för att hantera avvägningen. I denna rapport genereras först en upplänkskanal för ett fleranvändarsystem med flera ingångar med flera utdata. Fädningskanalen uppskattas av den autoregressiva modellen med hjälp av autokorrelations funktionen. Sedan beräknas signal till interferens plus brusförhållandet och spektral effektivitet som en funktion av effekttilldelnings förhållandet och andra parametrar för kommunikationsnätverket. Effektstyrnings algoritmen är att hitta den övre gränsen för den spektrala effektiviteten. I detta arbete modelleras också två obemannade flygfordonsnätverk och prestanda för effektstyrningsalgoritmen simuleras också på dessa två modeller för att hitta hur nätverkets parametrar kommer att påverka algoritmresultaten.

The objectives of this work were to investigate, design and implement Multiple-Input Multiple-Output (MIMO) antenna arrays for mobile phones. Several MIMO antennas were developed and tested over various wireless-communication frequency bands. The radiation performance and channel capacity of these antennas were computed and measured: the results are discussed in the context of the frequency bands of interest. A comprehensive study of MIMO antenna configurations such as 2 × 1, 3 × 1, 2 × 2 and 3 × 3, using polarisation diversity as proposed for future mobile handsets, is presented. The channel capacity is investigated and discussed, as applying to Rayleigh fading channels with different power spectrum distributions with respect to azimuth and zenith angles. The channel capacity of 2 × 2 and 3 × 3 MIMO systems using spatial polarisation diversity is presented for different antenna designs. The presented results show that the maximum channel capacity for an antenna contained within a small volume can be reached with careful selection of the orthogonal spatial fields. The results are also compared against planar array MIMO antenna systems, in which the antenna size considered was much larger. A 50% antenna size reduction method is explored by applying magnetic wall concept on the symmetry reference of the antenna structure. Using this method, a triple dual-band inverted-F antenna system is presented and considered for MIMO application. Means of achieving minimum coupling between the three antennas are investigated over the 2.45 GHz and 5.2 GHz bands. A new 2 2 MIMO dual-band balanced antenna handset, intended to minimise the coupling with the handset and human body was proposed, developed and tested. The antenna coupling with the handset and human hand is reported in terms the radiation performance and the available channel capacity. In addition, a dual-polarisation dipole antenna is proposed, intended for use as one of three collocated orthogonal antennas in a polarisation-diversity MIMO communication system. The antenna actually consists of two overlaid electric and magnetic dipoles, such that their radiation patterns are nominally identical but they are cross-polarised and hence only interact minimally.